1. Field of the Invention
This invention relates, in certain aspects, to systems and methods for forming an open hole section in a cased well and drilling a directional wellbore therefrom during a single trip into a wellbore.
2. Description of Related Art
For efficient and cost-effective recovery of hydrocarbons from a subterranean formation, it may at times be advantageous to drill a directional or branch wellbore from a location (“kick-off” point) along a cased main wellbore. Conventionally, the drilling of this directional wellbore, sometimes referred to as a sidetracking operation, requires the use of a number of different tools and multiple trips into the wellbore. As is known, a conventional bit (e.g., tri-cone bit) is not suited for cutting through the metal wall of a casing. Thus, a typical sidetracking operation begins by first assembling at the surface a work string provided with a suitable mill for cutting the metal wall of a casing to thereby form an open hole section in a cased wellbore. The work string provided with the mill is tripped into the wellbore, positioned at the anticipated kick-off point for the branch wellbore, and operated to remove casing material to form the open hole section. After the open hole section is formed, the work string is pulled out of the well bore and disassembled. To direct a BHA into the open hole section, many conventional methods use a device such as a deflector (e.g., a whipstock) below the open hole section. This deflector is positioned in the main wellbore using another work string that is tripped into and out of the wellbore. Thereafter, a drill string provided with a bottomhole assembly is tripped into the wellbore and guided into the open hole section by the deflector. Still another operation such as a drill-out or fishing operation may be needed to remove the deflector.
As is known, rig time is a factor in the cost of constructing a hydrocarbon producing well. The repeated assembly and disassembly of work string and tools used in conventional sidetracking operations increases rig time and thereby increases the cost to the well operator. Likewise, tripping work string and drill string thousands of feet into a well also consumes rig time and cost. Moreover, each trip-in or trip-out carries with it a risk of equipment failure (e.g., a tool becoming stuck in the hole).
The present invention addresses the need for a more efficient and effective single-trip milling method and systems for sidetracking and other similar operations.